In the past, some effort has been made to provide an alarm or the like which will warn miners and mine operators that some portion of a mine structure has made a substantial change or shift in the strata, and normally the alarm is activated after the change or shift has occurred. Also, the alarm ordinarily is either in an "on" condition or an "off" condition and does not signal an impending change nor shift in the geological structure of the mine. These alarms may be mounted on the roof supports which extend from the floor to the roof of the mine or may be attached to conventional roof support bolts which are embedded within the strata above the top of the mine.
Some examples of this type of structure are disclosed in U.S. Pat. Nos. 3,111,655 to Kortarsky, et al and 4,156,236 to Conkle.
Additional efforts, such as disclosed in U.S. Pat. No. 4,066,992 to Butler et al, have been made to provide a continuous surveillance system on the seismic disturbances in and around the mine in an effort to determine when a disturbance of sufficient magnitude to cause damage to the mine will occur.